Anthrax is an acute infectious disease caused by the bacterium B. anthracis. Anthrax mc commonly occurs in wild and domestic lower vertebrates (cattle, sheep, goats, camels, antelopes, other herbivores), but it can also occur in humans, for example, when they are exposed to infected animals or tissue from infected animals, or anthrax spores.
The virulence of B. anthracis is dependent on Anthrax Toxin (AT), and the poly-γ-D-glutamic acid capsule (γDPGA). The genes for the toxin, and the capsule, are carried by plasmids designated pX01 and pX02, respectively (Mikesell et al, Infect. Immun. 39:371-76, 1983; Vodkin al., Cell 34:693-97, 1983; Green et al., Infect. Immun. 49:291-97, 1985). AT is composed of three entities: Protective Antigen (PA) (the binding subunit of AT), and two enzymes known as Lethal Factor (LF) and Edema Factor (EF) (Mikesell et al., Infect. Immun. 39:371-76, 1983; Vodkin et al Cell 34:693-97, 1983). PA is an 83 kDa protein that is the main protective constituent of anthrax vaccines.
PA is necessary for vaccine immunogenicity (Ivins et al., Infect. Immun. 60:662-68, 1992; Welkos and Friedlander, Microb. Pathog. 5:127, 1998). Antibodies against PA prevent anthrax toxin from binding to host cells, thus abrogating toxicity (Little and Ivins, Microbes. Infect. 1:131-39, 1999). Additionally, antibodies to PA can inhibit the germination of spores while improving their phagocytosis and killing by macrophages (Welkos eta., Microbiology 147:1677-85, 2001). Unfortunately, the currently licensed human anthrax vaccine (AVA, BioPort Corporation, Lansing Mich.) requires six vaccinations over eighteen months followed by yearly boosters to induce and maintain protective anti-PA titers (Pittman et al., Vaccine 20:1412-20, 2002; Pittman et al., Vaccine 20:972-78, 2001). In some vaccines, this regimen is associated with undesirable local reactogenic (Pittman et al., Vaccine 20:972-78, 2001).
Thus, while certain prophylactic and treatment schemes may prove useful in preventing o directed toward anthrax. In particular, there is a need for an effective and safe vaccine that would require fewer doses to confer immunity to anthrax.